Many imaging devices employ automatic focus (AF) to allow for automatic adjustment of an imaging device to capture image data. For example, one conventional type of AF is based on depth from focus (DFF). Conventional methods of DFF typically capture image data for each focal position of a scene. The sharpness of each focal position may be then analyzed to determine the sharpest focal position, that is the focal position with the highest sharpness metric. As a result of the sharpness determination, the imaging device may automatically set the focus. This approach, however, requires capturing a plurality of images and results in a period of delay during automatic focus. In many instances, the processing delays of DFF do not suit many users of imaging devices, particularly portable imaging device such as digital cameras.
Another approach to automatic focus involves depth from defocus (DFD). Conventional methods and devices employing DFD are typically limited to stationary imaging devices. Further, these methods generally require modeling of blur information in order to determine automatic focus. As a result, parameters of the imaging device must be determined for each zoom and aperture state to allow for AF. These determinations are complicated and result in processing delays which do not suit many users of imaging devices. Accordingly, there is a need in the art for improved automatic focus which overcomes one or more of the aforementioned drawbacks.